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[2003:dc:6f1d:f00:230:64ff:fe74:809]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-61eaf5883b6sm255566a12.20.2025.09.01.05.30.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 01 Sep 2025 05:30:32 -0700 (PDT) From: Max Kellermann To: akpm@linux-foundation.org, david@redhat.com, axelrasmussen@google.com, yuanchu@google.com, willy@infradead.org, hughd@google.com, mhocko@suse.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, vishal.moola@gmail.com, linux@armlinux.org.uk, James.Bottomley@HansenPartnership.com, deller@gmx.de, agordeev@linux.ibm.com, gerald.schaefer@linux.ibm.com, hca@linux.ibm.com, gor@linux.ibm.com, borntraeger@linux.ibm.com, svens@linux.ibm.com, davem@davemloft.net, andreas@gaisler.com, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, chris@zankel.net, jcmvbkbc@gmail.com, viro@zeniv.linux.org.uk, brauner@kernel.org, jack@suse.cz, weixugc@google.com, baolin.wang@linux.alibaba.com, rientjes@google.com, shakeel.butt@linux.dev, max.kellermann@ionos.com, thuth@redhat.com, broonie@kernel.org, osalvador@suse.de, jfalempe@redhat.com, mpe@ellerman.id.au, nysal@linux.ibm.com, linux-arm-kernel@lists.infradead.org, linux-parisc@vger.kernel.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: [PATCH v5 00/12] mm: establish const-correctness for pointer parameters Date: Mon, 1 Sep 2025 14:30:16 +0200 Message-ID: <20250901123028.3383461-1-max.kellermann@ionos.com> X-Mailer: git-send-email 2.47.2 Precedence: bulk X-Mailing-List: sparclinux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit For improved const-correctness. This patch series systematically adds const qualifiers to pointer parameters throughout the memory management subsystem, establishing a foundation for improved const-correctness across the entire Linux kernel. Const-correctness provides multiple benefits: 1. Type Safety: The compiler enforces that functions marked as taking const parameters cannot accidentally modify the data, catching potential bugs at compile time rather than runtime. 2. Compiler Optimizations: When the compiler knows data won't be modified, it can generate more efficient code through better register allocation, code motion, and aliasing analysis. 3. API Documentation: Const qualifiers serve as self-documenting code, making it immediately clear to developers which functions are read-only operations versus those that modify state. 4. Maintenance Safety: Future modifications to const-correct code are less likely to introduce subtle bugs, as the compiler will reject attempts to modify data that should remain unchanged. The memory management subsystem is a fundamental building block of the kernel. Most higher-level kernel subsystems (filesystems, drivers, networking) depend on mm interfaces. By establishing const-correctness at this foundational level: 1. Enables Propagation: Higher-level subsystems can adopt const-correctness in their own interfaces. Without const-correct mm functions, filesystems cannot mark their own parameters const when they need to call mm functions. 2. Maximum Impact: Changes to core mm APIs benefit the entire kernel, as these functions are called from virtually every subsystem. 3. Prevents Impedance Mismatch: Without const-correctness in mm, other subsystems must either cast away const (dangerous) or avoid using const altogether (missing optimization opportunities). Each patch focuses on a specific header or subsystem component to ease review and bisection. This work was initially posted as a single large patch: https://lore.kernel.org/lkml/20250827192233.447920-1-max.kellermann@ionos.com/ Following feedback from Lorenzo Stoakes and David Hildenbrand, it has been split into focused, reviewable chunks. The approach was validated with a smaller patch that received agreement: https://lore.kernel.org/lkml/20250828130311.772993-1-max.kellermann@ionos.com/ Signed-off-by: Max Kellermann --- v1 -> v2: - made several parameter values const (i.e. the pointer address, not just the pointed-to memory), as suggested by Andrew Morton and Yuanchu Xie - drop existing+obsolete "extern" keywords on lines modified by these patches (suggested by Vishal Moola) - add missing parameter names on lines modified by these patches (suggested by Vishal Moola) - more "const" pointers (e.g. the task_struct passed to process_shares_mm()) - add missing "const" to s390, fixing s390 build failure - moved the mmap_is_legacy() change in arch/s390/mm/mmap.c from 08/12 to 06/12 (suggested by Vishal Moola) v2 -> v3: - remove garbage from 06/12 - changed tags on subject line (suggested by Matthew Wilcox) v3 -> v4: - more verbose commit messages including a listing of function names (suggested by David Hildenbrand and Lorenzo Stoakes) v4 -> v5: - back to shorter commit messages after an agreement between David Hildenbrand and Lorenzo Stoakes was found Max Kellermann (12): mm: constify shmem related test functions for improved const-correctness mm: constify pagemap related test functions for improved const-correctness mm: constify zone related test functions for improved const-correctness fs: constify mapping related test functions for improved const-correctness mm: constify process_shares_mm() for improved const-correctness mm, s390: constify mapping related test functions for improved const-correctness parisc: constify mmap_upper_limit() parameter for improved const-correctness mm: constify arch_pick_mmap_layout() for improved const-correctness mm: constify ptdesc_pmd_pts_count() and folio_get_private() mm: constify various inline test functions for improved const-correctness mm: constify assert/test functions in mm.h mm: constify highmem related functions for improved const-correctness arch/arm/include/asm/highmem.h | 6 +-- arch/parisc/include/asm/processor.h | 2 +- arch/parisc/kernel/sys_parisc.c | 2 +- arch/s390/mm/mmap.c | 7 ++-- arch/sparc/kernel/sys_sparc_64.c | 3 +- arch/x86/mm/mmap.c | 7 ++-- arch/xtensa/include/asm/highmem.h | 2 +- include/linux/fs.h | 7 ++-- include/linux/highmem-internal.h | 44 +++++++++++---------- include/linux/highmem.h | 8 ++-- include/linux/mm.h | 56 +++++++++++++-------------- include/linux/mm_inline.h | 26 +++++++------ include/linux/mm_types.h | 4 +- include/linux/mmzone.h | 42 ++++++++++---------- include/linux/pagemap.h | 59 +++++++++++++++-------------- include/linux/sched/mm.h | 4 +- include/linux/shmem_fs.h | 4 +- mm/highmem.c | 10 ++--- mm/oom_kill.c | 7 ++-- mm/shmem.c | 6 +-- mm/util.c | 20 ++++++---- 21 files changed, 171 insertions(+), 155 deletions(-) -- 2.47.2